Field of the Invention
The present invention relates to an oxygen storage material comprising composite oxides and a method for producing the same.
Related Background Art
Composite oxides containing various metal oxides have heretofore been utilized as supports, promoters, and the like for catalysts for purification of exhaust gas. As the metal oxide in such a composite oxide, ceria has been preferably used because ceria is capable of storing and releasing oxygen according to the partial pressure of oxygen in an atmosphere (i.e. having an oxygen storing capacity). In addition, various kinds of composite materials containing ceria have recently been studied.
For example, Japanese Unexamined Patent Application Publication No. 2005-231951 (Patent Literature 1) discloses a composite oxide having a pyrochlore structure containing Ce and Zr, wherein 40 to 90% of Ce is substituted by ions of a rare earth metal other than Ce or ions of an alkaline earth metal. Patent Literature 1 also states that this composite oxide is excellent in oxygen storage/release performance. However, since the composite oxide comprises one kind of a pyrochlore-type composite oxide, the composite oxide does not have a sufficiently high oxygen storage/release rate.
Meanwhile, Japanese Unexamined Patent Application Publication No. 2014-114180 (Patent Literature 2) discloses a composite oxide material comprising: crystal particles having a pyrochlore structure of a ceria-zirconia composite oxide; and a crystal having a pyrochlore structure of a lanthana-zirconia composite oxide present on surfaces of the particles, wherein the crystal of the lanthana-zirconia composite oxide is at least partially solid-dissolved in the surfaces of the crystal particles of the ceria-zirconia composite oxide. Patent Literature 2 also states that this composite oxide material is excellent in stability at high temperature.